Survivability and structural requirements in advanced aircraft require cooling and thermal management of aircraft and propulsion structures. Additionally, some applications of aircraft technology, particularly those applications on supersonic aircraft, require sources of cooled, high pressure air. Conventional methods for propulsion system cooling in current aircraft engines typically employ either engine fuel, or air from one of the various sources in the propulsion system as a coolant. Among the traditional sources of cooling air are 1) ram air from the inlet, 2) air from the fan (in turbofan engines), or 3) air from the high compressor.
These sources for cooling air have generally been adequate for cooling aircraft components up to this time, the cooling air being primarily used for maintaining structural integrity of engine components. Although cooling air diverted from the aforementioned sources impacts overall engine performance, the cooling requirements have heretofore been achieved with only minimal impact on engine performance. However, as the amount of electronic and other heat generating equipment carried on aircraft has increased, the requirement for cooling system capability has correspondingly increased. In addition, as aircraft speeds and capabilities increase beyond about Mach 3, the demands on the cooling systems of aircraft increase as well. These increased speeds and capabilities require cooling of aircraft components such as leading edges of the airframe, and certain parts of the engine exposed to high temperature combustion products. Additionally, new uses of cool, high pressure air on aircraft increase the demand for such air beyond that amount that is currently available. The increasingly stringent requirements for future vehicle/engine systems will require improved sources of low temperature coolants.
What is needed is a method for producing cooled air at relatively high pressure, and at other relatively lower pressure as needed by the aircraft components and engines without substantially increasing the amount of cooling air diverted from the traditional sources of cooling air.